1. Field of the Invention
The present invention relates to systems for evaluating and measuring the performance of lithographic structures, and more particularly to a system for monitoring the optical parameters of a projection lithography system which uses the instant electrical readout from an array of photosensitive detectors fabricated on a silicon wafer in combination with a computer for real-time characterization of lithographic devices and the evaluation of optical E-beam, ion-beam and X-ray parameters.
2. Description of the Prior Art
The general use of photosensitive detectors fabricated on silicon to monitor optical systems has been described in the prior art. A list of typical prior art references is as follows:
DiStefano IBM Technical Disclosure Bulletin, Vol. 23, No. 12, May 1981, at page 5601. PA0 Foisy et al, IBM Technical Disclosure Bulletin, Vol. 25, No. 7B, Dec. 1982 at page 3654. PA0 Chi et al, IBM Technical Disclosure Bulletin, Vol. 25, No. 10, March 1983 at page 5052. PA0 Jacobus et al, IBM Technical Disclosure Bulletin, Vol. 13, No. 8, Jan. 1971 at page 2322. PA0 U.S. Pat. No. 4,329,049 PA0 U.S. Pat. No. 3,938,894 PA0 U.S. Pat. No. 4,281,927 PA0 U.S. Pat. No. 4,354,104 PA0 U.S. Pat. No. 3,969,751 PA0 U.S. Pat. No. 3,988,774 PA0 U.S. Pat. No. 4,184,894 PA0 U.S. Pat. No. 4,021,844.
The DiStefano publication describes a method for doing optical detection on a silicon detector device. The detector consists of a plurality of detector cells each containing two p-n junction elements.
The U.S. Pat. No. 4,329,049 patent teaches the use of an electrically scanning linear photodiode array in combination with a computer for determining the refractive properties of a lens.
The U.S. Pat. No. 3,938,894 patent discloses the use of a plurality of photodiodes on a substrate to detect the focus condition of a lens.
The Foisy et al publication shows a means for the measurement of the modulation transfer function of image sensing photodiode arrays.
The Chi et al publication discloses an optical method to replace electrical device testing.
The U.S. Pat. No. 4,281,927 patent teaches a focusing technique utilizing a photocell which is scanned by a rotating disc.
The other remaining patents and publications disclose other photodiode and photoconductor structures including the use of light-shielding means.
What is different in the present invention over the prior art is the use of a unique mask with the radiation-sensitive detectors in combination with compiling means for the purposes of evaluating image projection from a lithographic system, including the properties of intensity, modulation transfer function (MTF), focus and alignment.